What on earth does the 7.6 inches / 20 cm requirement refer to?!

I just got my new SmartThings hub and a leak detector sensor. Reading the manual, I see on the “Simple Setup” page this wording: “The SmartThings Hub works best if installed in a central location to where your SmartThings will be connected” . Fair enough - not really practical since the hub has to be hardwired (ethernet cable) and most people aren’t going to have a centrally located ethernet switch, but let’s not dwell on that one! The next sentence is “The recommended separation distance from the user for this equipment is 7.6 inches (20 cm)”. What ON EARTH is this telling me?! What is ‘the user’ in this context?

Is this telling me I need to have things within 7.6" for them to work? Can’t possibly mean that. Is it telling me that for safety/radiation concerns I should locate the device at least 7.6" away from a human being? I mean, there really isn’t any context provided in that paragraph!

I decided to ignore this sentence and forge ahead, and got everything working despite my various devices being 20+ feet away … so I’m all set; I just can’t make sense out of that sentence!

By the way, I found another topic similar to this but for the life of me could not find it when I came back to look for it. This forum software is different from any forum software I’ve ever used before. Sure looks sexy and different … but I think I’d prefer a simple vbulletin type environment! I’m sure I’ll get used to it :slight_smile:

1 Like

Google the above quote and you’ll find it filed with FCC documents, etc…

Indeed, unlike a cell phone held next to your ear or in your pants…, for perhaps an abundance of caution, RF radiation safety levels may exceed idea level of risk to persons within 20cm of the Hub.

1 Like

Though… maybe 20cm / 7.6" is a magical number for non-RF related clearance as well.

The Cisco 300 Manual refers to this distance for airflow


But… Honeywell’s point-to-point Wireless Hazardous Area limit switch mentions…




I did google the quote, and just did so again; I see the phrase occurring in online copies of the manuals, and I do see an FCC site link, but it’s just a repeat of the statement, in the context of the manual. - https://fccid.io/document.php?id=2570588 . So I’m still not seeing any context as to what it’s really trying to tell me. I’m totally on board with your explanation, which is what I was guessing at, but really - it’s not the clearest of warnings!

If the word ‘minimum’ was used, or ‘at least’ … that would help clarify. But by saying ‘recommended separation’, one could assume that is an actual recommendation. Since it was in the section on Simple Setup, and I was about to ‘pair’ my first device, I actually wondered if it was telling me to place the ‘to be paired’ item at the ‘recommended separation’.

But regardless - you mentioned cell phones; I presume the potential for human damage from a cellphone is significantly greater than the potential from the SmartThings hub, given the the hub is only able to communicate within a few feet, compared to a cell phone which can communicate over much greater distances?

1 Like

That’s a reasonable presumption.

The reality? The FCC is a government organization that the cell phone industry has successfully lobbied to minimize warnings on cell phone RF risks.

The “20 cm” risk/safety radius is probably just a blanket value used based on a specific single or set of scientific studies which they require all manufacturer / vendors to include in their documentation, in order to receive FCC certification. The wording need not be meaningful … it just needs to be included.

Laws are stupid. :crazy_face:

1 Like

Standard FCC radio frequency exposure requirement.

Basically any device intended to be worn/used close to the body, such as headphones and some medical equipment and mobile phones, is required to have additional shielding to reduce the longterm tissue impact of the radio transmissions.

Devices not intended for this purpose don’t have to have the extra shielding, but then they have to have the warning message saying that you’re not supposed to be using it that close on a regular basis.

It doesn’t mean you can’t pick it up and carry it while it’s operating, or occasionally do something closer to it. It just means that it’s not intended for frequent use close to the body. Like @anon36505037 said, don’t mount the hub on the headboard of your bed. :wink:


15 into the hub and 15 out again when using the ZHA 1.2 profile that SmartThings uses. With a strong mesh you shouldn’t see any noticeable speed difference, though, all the transmissions are fast.


As others have said, it is a legally required notification. You can make your own choices, but the requirement to notify has been satisfied. Personally, I wouldn’t be too concerned, but YMMV.

Example: back in the day, a tower monkey changing light bulbs on a series-fed commercial AM broadcast tower might set up a wooden stepladder next to the tower and jump over to the tower and climb it live. Today, that same station must shut off the transmitter before anyone climbs the tower (or switch to a ‘backup’ tower if one exists). All because of the perceived danger of near-field RF exposure at those frequencies.

We’re a lot more knowledgeable these days about the effects of RF radiation on the human body…

1 Like

Yep. These days the potential danger is evaluated based on a combination of:


Signal strength

Magnetic field strength

Distance from the person

Time of exposure

A stronger field farther away that you just walk past may be less damaging than a much weaker field in a device worn on your wrist for hours every day.

1 Like

I lolled at your title selection. :nerd_face:

… I must be a bit tired I guess!


I never worry about carrying my cell phone in my pocket, because I had a vasectomy.

DO YOUR WORST, RF!!! :smiley: